1. Field of the Invention
The invention relates to the field of automobile service lifts, and in particular to a safety lock mechanism for a post-type lift having a lifting carriage slidably mounted to a vertical post or column and supported by a chain, cable, or other flexible lifting member.
2. Description of the Related Art
A wide variety of post-type automobile lifts have been previously known and used in the automobile repair business to provide access to the underside of a vehicle. Post lifts can be either of the in-ground or above-ground variety. In-ground post lifts usually have one or two vertically ascending columns mounted below the floor of a garage or service area which are raised hydraulically to lift the vehicle. Above-ground post lifts generally have two or four vertical columns or xe2x80x9cposts,xe2x80x9d each of which includes a lifting carriage which rides up and down the post and has one or more arms for engaging and raising the vehicle. These lifting carriages are often raised and lowered by means of a chain, cable, or other flexible lifting member which is driven by a winch or hydraulic actuator.
It has long been known to provide automobile lifts with a ratchet lock mechanism to prevent unintentional lowering of the lifting carriages, which could result in injury to the lift operator or damage to the vehicle or other property. These devices generally include a ratchet track, with a plurality of vertically spaced teeth, which is connected to the post and a ratchet pawl which is pivotally connected to the lifting carriage and selectively engages the ratchet track. When engaged, the ratchet lock mechanism allows the lifting carriage to be raised, but prevents it from being lowered. In order to lower the lifting carriage, the ratchet pawl must be manually disengaged from the ratchet track. A problem with some of these ratchet lock mechanisms is that in order for the mechanism to work, the ratchet must be manually re-engaged before the lift is raised again after being lowered.
If properly engaged, the ratchet lock mechanism will operated to prevent the lifting carriage from falling while the lift is being raised, but it cannot by itself provide an adequate level of safety because it must be disengaged to lower the lift. If one of the flexible lifting members should break while the lift is being lowered or at anytime when the ratchet lock is inadvertently left in the disengaged position, there is nothing to keep the respective lifting carriage from falling all the way to the bottom of the post. In order to provide complete safety, a safety lock device for an automobile lift should include a fail-safe mechanism which automatically re-engages the ratchet lock mechanism in the event that one of the flexible lifting members should break or otherwise becomes slack.
Several safety lock devices incorporating fail-safe devices have been previously known. U.S. Pat. No. 2,238,573 to E. H. Steedman discloses a winch and cable operated automobile lift having a fail-safe device wherein each cable is connected to a crank member which is pivotally attached to the inside of the lifting carriage. A spring provides tension which acts in opposition to the cable tension. Should the cable break, the spring tension would cause the crank member to rotate about its mounting point, allowing a dog on the crank member to engage one of a series of holes cut into the back side of the post, stopping downward travel of the carriage. A second patent to Mr. Steedman, U.S. Pat. No. 2,266,915 discloses a fail-safe mechanism comprising an escapement-type ratchet mechanism which is locked by means of a counterweight if the carriage begins to descend too quickly. While the safety devices disclosed by the Steedman patents provide fail-safe mechanisms designed to prevent the lift from falling in the event of a broken cable, they contain no provisions for preventing accidental of unintended lowering of the lift in the absence of such a mechanical failure.
U.S. Pat. No. 4,331,219 to Yasunori Suzuki discloses a safety device for a chain operated lift which includes a ratchet track attached to the column and a pawl pivotally connected to the carriage by a pivot rod. When the lift is being raised, the pawl is biased into an engaging position with the slot plate by a torsional spring. During lowering of the lift, the pawl is held in a disengaged position by a latching plate which is pivotally connected to the carriage and engages the tang of an action plate connected to the pawl pivot rod. The lifting chains are connected to the carriage by a suspension rod, and a coil spring acts on the suspension rod in opposition to the chain tension. A push rod connected to the suspension rod has a distal end in contact with the pawl latching plate. If the chain were to break, the coil spring would push the suspension rod and push rod downward, thereby pivoting the latching plate and releasing the action plate. The torsion spring would then rotate the pawl pivot rod and the pawl into the engaging position and prevent downward movement of the carriage.
The ratchet lock of the Suzuki lift is also equipped with a push rod connected to the pawl latching plate which has a distal end which engages the floor when the lifting carriage is fully lowered and automatically resets the pawl to its engaging position. This feature partially solves the problem of a lift operator forgetting to engage the ratchet lock before raising the lift, but it is only operative if the lift is lowered completely to the floor. It would still be possible for the operator to disengage the lock, partially lower the lift (to access another portion of the vehicle, for instance) and then raise the lift again without re-engaging the ratchet lock.
U.S. Pat. No. 4,457,401 to James J. Taylor, et al. discloses a chain operated hydraulic lift having a ratchet lock mechanism which includes a ratchet track welded to the post and a pawl pivotally connected to the carriage. The pawl is biased into a position engaging the ratchet track by a spring. The pawl is released by a foot pedal which applies tension to a cable connected to the pawl. The safety lock device also includes fail-safe mechanism which includes a chain tension sensing mechanism mounted at the top of the post. The chain sensing mechanism includes a pulley which is connected to the pawl release cable. If the chain breaks and thereby loses tension, the chain tension sensing mechanism is triggered, pivoting the pulley downward and releasing the tension on the pawl release cable, thereby causing the pawl to pivot into the engaging position and preventing downward movement of the carriage.
While the Taylor lift does provide a fail-safe mechanism in combination with a ratchet lock which automatically resets (the ratchet pawl returns to the engaging position when the operator releases the foot pedal), it does so at the expense of making the operator stand in close proximity to the lift to keep the foot pedal depressed while the lift is descending, thereby increasing the likelihood of personal injury.
It is clear that there remains a need for a safety lock device which has both a ratchet lock device to prevent inadvertent lowering of the lift and a fail-safe device to engage the ratchet lock in the event of a flexible lifting member failure during lowering, the ratchet lock being designed so that it automatically re-engages itself anytime the lifting carriage begins to move upwardly.
The present invention comprises a safety lock device for an automobile lift having a lifting carriage slidably connected to a post and supported by a flexible lifting member, such as a chain or cable. The safety lock device comprises a ratchet lock mechanism which prevents inadvertent lowering of the carriage and a fail-safe mechanism which automatically engages the ratchet lock in the event that the flexible lifting member should fail or otherwise become slack while the ratchet lock is disengaged.
The ratchet lock mechanism includes a ratchet track which is connected to the post and a ratchet pawl which is connected to the lifting carriage and is pivotable between a track engaging position and a release position. The pawl is biased into the track engaging position by a spring. When the ratchet pawl is in the track engaging position, the pawl allows the lifting carriage to move upward but prevents it from moving downward.
The pawl is moved into the release position by a pawl release lever which is pivotally connected to the ratchet pawl. The release lever has first and second ends, the first end being located proximate the post, and is pivotable about a point intermediate the first and second ends between a first position and a second position. In the first position, the release lever first end is out of engagement with the post and the ratchet pawl is retained in the track engaging position by the spring, whereas in the second position the release lever first end engages the post so as to push the pawl away from the post and pivot the pawl into the release position.
The ratchet lock mechanism is automatically engaged upon upward movement of the lifting carriage, since such upward movement with the pawl release lever in the second position causes the pawl release lever first end to pivot downwardly, moving the pawl release lever into the first position and thereby allowing the pawl spring to urge the ratchet pawl into the track engaging position.
The fail-safe mechanism includes a flexible member connector which is mounted to the lifting carriage and is slidable between an upper position and a lower position. The flexible lifting member is attached to an upper end of the flexible member connector such that tension in the flexible lifting member holds the flexible member connector in the upper position. A spring connected to the flexible member connector acts in opposition to tension in the flexible lifting member and urges the flexible member connector into the lower position upon loss of tension in the flexible lifting member. A trip lever connected to the lifting carriage below the flexible member connector has a first end in contact with the flexible member connector and a second end connected to the pawl release lever. The trip lever is pivotable with respect to the lifting carriage about a point intermediate its first and second ends such that the first end moves downwardly and the second end moves upwardly as the flexible member connector moves from the upper position to said lower position. The upward movement of the trip lever second end pivots the pawl release lever into its first position, allowing the pawl to be pivoted into the track engaging position by its spring.
The principal objects and advantages of the present invention include: providing a safety lock device for an automobile lift which prevents inadvertent lowering of the lift; providing such a safety lock device which includes a fail-safe mechanism which automatically engages the safety lock upon failure of a flexible lifting member; providing such a safety lock device which automatically engages the safety lock upon upward movement of the lift; providing such a safety lock device which can be fully contained and protected within the structure of a lifting carriage of the lift; and providing such a safety lock device which is economical to manufacture, efficient in operation, capable of a long operating life and particularly well-adapted for the proposed usage thereof